I assume you mean by “balanced standard” that there are conpanies that
incorporate XLR jacks but that they have single ended circuitry, as
opposed to fully balanced designs such as those by Ayre and Aestestix?
Actually no. A component can support the balanced standard and be internally single-ended. In such a case transformers are used to convert from one to the other.
The balanced standard has to do with how the signal moves from one piece to the other. Here it is in a nutshell:
1) pinouts: pin 1 is ground, pin 2 is non-inverted, pin 3 is inverted (pins 2 and 3 are reversed in Europe)
2) Ground is **ignored**. This means that the pin 2 and 3 signals do not reference ground; instead they reference each other. This is where the vast majority of high end audio products fail to meet the standard. For example ARC has the pin 2 and 3 outputs, but each one references ground to complete the circuit. This is important as this puts signal currents in the shield, which isn't supposed to have any, otherwise ground loops can result and the construction of the cable can also be a lot more audible. Output transformers do this by having no center tap and just a simple secondary (if an output) connected to pins 2 and 3 and nothing else.An input transformer does this by having its primary connected again to just pins 2 and 3 and nothing else. Pin 1 in both cases is simply ground.
3) the system is low impedance- 600 ohms used to be the old standard; these days its considered adequate if the balanced output can drive 2000 ohms or less. For this reason the line stage is essentially a small power amplifier. The resulting low impedances also help prevent noise pickup, longer cable lengths (although the benefit is there even if the cable is only 6 inches) and immunity to the cable itself, allowing the system to be less colored and more musical.
